.trans {
  transition: transform .2s ease;
}

@size: 40px;

.sider-trigger-a {

  width: @size;



  display: flex;
  height: 100%;
  align-items: center;
  justify-content: center;
  color: #5c6b77;

  i {
    .trans;
    vertical-align: top;
  }

  &.collapsed i {
    transform: rotateZ(90deg);
    .trans;
  }
}